The invention relates to a cutting apparatus and method, in particular for cutting or engraving plastics or metal (for example aluminium or steel), more in particular to make a weakening line in caps made of plastics.
Specifically, but not exclusively, the invention can be used to produce caps made of plastics for closing containers, in particular for making the preferential weakening or fracturing line that is used to define a tamperproof device intended to indicate the first opening of the cap.
Making the preferential breaking line of a tamperproof ring in caps made of plastics by cutting apparatuses that comprise a carousel that has a series of movable spindles that are able to rotate around their axis is known. In use, the caps to be cut engage in the spindles and are thus rolled on a fixed sector that carries a blade that is suitably shaped according to the type of cut that it is desired to perform. The fixed sector can be positioned either outside the carousel that carries the spindles or inside the spindles.
One of the problems of the known apparatuses of this type is of the fact that the cutting blade is subject to wear during use and can accidentally splinter or break, with consequent deterioration in the quality of the caps produced, such that the correct operation of the tamperproof device is no longer ensured.
This problem is particularly relevant in the case of a machining process that occurs continuously and in line with other apparatuses.
Solving the above problem by means of periodical checking of the cutting quality on the caps produced and thus of the correct function of the tamperproof device is known, by removing and checking a sample at periodical intervals (for example every one or two hours). This solution nevertheless has the following drawback: if for example average production speed is 60,000 caps an hour and the sampling period is one hour, if insufficient quality is detected in the sample of caps all the 60,000 caps produced in the hour preceding the sampling have to be rejected because correct operation of the tamperproof device would not be guaranteed.
The prior art further includes U.S. Pat. No. 4,511,054, which discloses a method and an apparatus to control the quality of the weakening line made between the tamperproof ring and the ‘skirt’ portion of a cap made of plastics. U.S. Pat. No. 4,511,054 relates to the problem of improving and controlling the dimensional tolerances of the weakening lines that are made on caps made of plastics. The apparatus and the method shown in this document perform a check directly on each cap. In particular, an optical apparatus is provided comprising a light source and a detector. During the test, the light source is positioned inside a cap while the detector is positioned outside the cap. The cap is rotated around an axis thereof while a light beam generated by the light source traverses a cap cutting zone and intercepts the detector. Each uncut cap portion is detected through an interruption of the light beam. The optical apparatus is able to detect whether the cutting zones meet preset dimensional parameters.
The use of laser devices for controlling the positioning and possible damage to or wear of a cutting blade is also known, as is the use of laser devices for controlling the flatness of a disc blade.
European Patent No. EP 1 609 570 disclosed a system for controlling the cutting blade, particularly for shearing machines for cutting sheets of paper, plastics, etc. The system has the function of continuously controlling friction wear or overheating deformation of a disc or hand blade for cuffing the sheet material. The system enables the cutting operation to be stopped at the moment in which an operationally unacceptable blade condition is detected. Measuring sensors (not shown) are provided that detect the variations in the radius of the blade caused by wear. A device is also provided for measuring the planar deformation of the blade, including a distance sensor, for example a laser probe provided with a transmitter/emitter coupled with an optical detector/receiver.
German Patent No. DE 4 232 236 disclosed a device for detecting the contour of a tool, such as a knife, a drill, etc. without contact. This document discloses the use of a laser device to check the contour of a tool. The device includes a laser source configured for generating two laser beams, and a detector suitable for receiving the two laser beams. During operation, the laser beams strike the side surface of the tool and from the manner in which they are intercepted by the detector the contour of the tool is detected point by point in space. A device that is similar to the one that has just been discussed is also shown in U.S. Pat. No. 4,657,395 and Japanese patent No. JP 62006114.
Japanese patent publication No. JP 54109682 discloses a method and a device for automatically detecting possible damage to a blade, in which a laser beam emitted by a light projector hits the surface of the blade and is reflected at 45 degrees to the hit surface. The reflected beam may or may not be intercepted by the receiver, which produces a significant signal of the state of damage of the blade. Depending on this signal, the system is stopped or continues to operate.
U.S. Pat. No. 6,237,455 discloses a cutting machine relating to the woodworking industry, provided with knives and with a detecting device for inspecting the knives. In one embodiment (FIGS. 6 and 7) the machine includes an annular rotor that internally supports in a cantilevered manner several knives and through rotational motion drags the knives to cut the pieces of wood. Two sensors are provided that are arranged at opposite ends to the knives and monitor how much the knives project towards the longitudinal axis of the annular rotor. The sensors may be proximity sensors. The sensors are arranged in a stationary position while the knives are moved.
U.S. Pat. No. 6,576,531 discloses a method and an apparatus for detecting incorrect positioning of a disc blade. A distance sensor, for example of laser type, is provided, which measures a distance from the disc blade while the latter rotates by detecting the variation of this distance, which has to be contained within a given range for correct operation of the system.
Patent publication WO 2004/004993 shows a cutting apparatus.